Catheters vary in construction and materials, such as providing a wire braid reinforced lumen or an inner lumen of greater rigidity than the outer lumen. Similarly, catheters vary in size from a few French (1 French=0.013 inch) to 50 French. Steerable catheters, unlike diagnostic catheters, generally do not have any reinforcement to provide torque characteristics. As such, steerable catheters are guided into the vasculature and to the area of interest in the vasculature over steerable guidewires which possess the necessary rigidity to transfer torque.
Access to the vasculature of interest is impaired due to the tortuous pathways and the small diameter vessels encountered. Furthermore, the application of radiopaque dye for diagnosis, and insertion of balloon and laser appliances for unblocking obstructions require the positioning of atraumatic and/or steerable elements for location of the area of interest. Such diverse requirements leads to the creation of complex catheter/guidewire structures. However, the need to reach the small diameter vessels results in a catheter structure limited to a specific function, and is often constructed in a manner which prohibits the exchange of guidewire or other coaxially related structure at the vessel site without complete withdrawal of the catheter. Furthermore, similar limitations with respect to the deployment of the guidewire exists, such that existing structures discourage guidewire or catheter exchanges while the other remains in place. For instance, guidewires having a balloon at the distal end are initially applied to reach and pre-dilate lesions, withdrawn and followed by the insertion of a balloon catheter to complete the dilation. Such structural limitation actively discourage complete therapy and introduce significant procedural complications and/or risk to the patient.